“The ability to eat meat allowed us to spread around the world as we didn't need to evolve to eat the plants in each area we immigrated to.”
It makes no sense that humans could evolve that quickly to adapt to a colder environment. The Inuit mummies Found in Greenland had osteoporosis, and archaeologists have proven that the Inuit diet is even worse than the standard American diet. But even the civilizations dwelling in the coldest parts of the world were able to eat seaweed, berries, wheat, potatoes, and even moss.
“Also, it can be quite difficult to get proper nutrition on a vegetable diet, especially when you are poor or have long winters where you live.”
Not at all. Plants have all of the nutrients we need, plant food is cheaper than flesh is, and we already have supermarkets. And remember that the low meat prices are actually a result of subsidization.
“Also, it is possible for individuals to raise animals that do not compete for human sources of food or even hunt for meat.”
I know that only cattles eat grass, but the pastures would be able to feed so many more folks if plants were grown there for human consumption. Hunting is not nearly as bad as is factory farming, but humans are not natural predators in any ecosystem. All invasive species (including humans) resulted from human activities, not from a lack thereof.